Ram Air Turbines (RATs) can be used in commercial aviation as emergency power systems. They typically have a turbine with a rotating hub and a plurality of blades. Initially in flight they are stowed in a compartment of the aircraft, covered by a compartment door. When called as a source of emergency or supplemental power, they commonly swing out through a narrow door opening.
Commercial aircraft manufacturers install ram air turbines (RATs) as an emergency form of power when the main engine generators (and/or hydraulic pumps) are not operating. When called upon for electrical power, the RAT is deployed into the airstream and functions similar to windmills by extracting energy from the flowing air along the aircraft in flight. As commercial aircraft become more complex and use more electrical power, the power generating requirements of the RAT have also increased. While technological improvements have made it possible to generate significantly more electrical power in a turbine-generator that is about the same size as prior lower power RATs, the amount of heat generated increases roughly in proportion to the increase in power capability. Therefore, the heat dissipation required to maintain a higher power RAT has also increased. In the past, the lower power RATs have been cooled by deploying the generator in an open type configuration and locating it at the turbine end of the RAT so that ambient airflow in the airstream of the aircraft can directly cool the windings and rotor of the generator. However, with heat dissipation requirements rising as much as five fold or more, ambient airflow cooling is no longer sufficient to maintain the temperature of the generator at an acceptable level. Moreover, in recent years, aircraft manufacturers have required sealed generators so that internal components and electrical circuits are protected against severe environmental conditions. Sealed generators exacerbate the cooling problem because the airflow cannot directly contact the interior of the generator. A sealed RAT generator on the Boeing 777 aircraft employs cooling fins on the exterior housing of the generator. However, that generator produces only about 7.5 Kilowatts at 4,000 RPM. Newer RAT generators will be required to produce up to about 50 Kilowatts at 12,000 RPM by using a gearbox between the RAT turbine and the RAT generator. The commensurate increase in generated heat (i.e., about seven fold) makes it imperative to provide more effective generator cooling than is practical using ambient airflow. Thus, there is a need to improve generator cooling in ram air turbine systems having higher power density generators that will be deployed in future aircraft.
U.S. Pat. No. 6,127,758, Ram Air Turbine System, is for a ducted ram air turbine where an output shaft drives both an electrical generator and a turbocompressor all within a pod. The term xe2x80x9cpodxe2x80x9d typically refers to an auxiliary assembly which attaches under the wings of military aircraft, similar to munitions but can be anything from an extra fuel tank to antenna jamming devices.
This patent refers to cooling of the electronic equipment within the pod by three different methods. The first method is to allow a portion of the ram air to enter the electronics cavity of the pod and passively cool the electronic equipment. The second method is to direct the cool ram air through a liquid cooling loop heat exchanger, where the coolant provides a heat sink for the electronic equipment. The third method is where ram air is expanded through the turbine side of the turbocompressor. This cooled air is then directed through the same liquid cooling loop heat exchanger. For the liquid cooling loop in this patent to work there does need to be some type of pump in the cooling loop to circulate the fluid, but no mention of pump is made in the patent. Moreover, the liquid cooling loop is independent of the ram air turbine.
U.S. Pat. No. 6,092,360, Ram Air Turbine System, teaches a passive cooling system where ambient air is used to cool an auxiliary power unit (APU). This patent outlines how air is drawn into the auxiliary power unit compartment of an aircraft, passing through the unit, then ducted overboard. The ambient air is moved by a device called an eductor, which uses APU exhaust flow to draw the ambient air into the compartment.
U.S. Pat. No. 24,179, Electric Generating And Air Cooling System, is a complicated electrical generating system. This patent refers to cooling a generator, but only passively by air blowing over the generator housing. To move the cooling air over the generator housing, a fan is affixed to the end of the rotating generator shaft. There is a ram air cooled heat exchanger described in the patent, but it is used to cool the hydraulic fluid of the system, not a liquid cooling loop.
In order to supply adequate cooling to the higher power RAT generator, this invention provides a self-contained cooling loop. This cooling loop includes a pump, heat exchanger, and cooling jacket integral to the generator housing. The cooling fluid may be the lubrication oil used within the gearbox that provides the substantially increased rotation rate of the generator.
The cooling is self-generating and independent from other aircraft systems. In the illustrated embodiment, a pitot pump within a gearbox may be used to circulate the oil in an active coolant loop. Pitot pumps are seldom used in gearbox lubrication systems, as it is more common to employ a positive displacement pump such as a gear pump or a gerotor type pump. A pitot pump is the preferred pump because of the possible cold starting conditions and the low flow requirement within the cooling loop. However, other pumps of suitable size and configuration could also be used as contemplated herein. The oil is first moved through the generator to remove excess heat, then flows through a heat exchanger where the ram air flows through to extract the heat.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, drawings and claims.